The aeroacoustic field generated by incompressible airflow over a two-dimensional open cavity is investigated. The main objective of this study is to determine the role of nonlinearity on this phenomenon. To this end the cavity aeroacoustics is investigated with both linearised and nonlinear approaches. Both free-air and confined cavity geometries are investigated and it is shown that nonlinearity does not affect the aeroacoustic field much. The solutions are verified for grid and computational domain independency. It is concluded from this study that nonlinear aeroacoustic phenomena are very weak in external incompressible flows and low-cost linearised formulations can easily be applied in such cases.